Current fiber composites have either good mechanical properties with less formable consistency or good formability with poor mechanical properties. In cases where the impregnated composites need to be pushed between teeth or formed therein, the fibers tend to fray resulting in difficult manipulation. The fraying of the fibers also occurs when the strips are cut into small pieces. One cause of the problem is the high elastic memory of the reinforcing fibers, which are frequently fabricated of fiberglass.
The fraying may be minimized by using heat treated woven tape made of fiberglass as set forth in U.S. Pat. No. 6,381,989 B1 to Karmaker et al., which is hereby incorporated by reference. However, the woven structure does not provide adequate mechanical properties as continuous fiber would and, therefore, is not suitable for many applications where higher strength is required such as in dental bridges.
Another approach involves embedding woven cloths of organic/inorganic fibers as disclosed in U.S. Pat. No. 6,114,409 to Krebber, which is hereby incorporated by reference. Products based on U.S. Pat. No. 6,114,409 include cloths of organic fibers such as polyethylene and polyester, embedded into highly filled dental composites. Some of the drawbacks of these products may be: a) the organic fibers do not provide satisfactory adhesion to the dental resin and therefore are prone to delamination; b) three-point bend test results have shown that products made of polyethylene and polyester embedded into highly filled dental composites have an average flexural strength of about 72±19 MPa that is even lower than many particulate filled composites; c) the fiber content is low in order to keep good formability, thus any reinforcing effect is also very minor; d) if inorganic fibers such as fiberglass are used, the amount of filled resin content has to be much higher in order to suppress the high elastic memory of such fibers and consequently will not provide adequate strength.
In another attempt, U.S. Pat. No. 6,197,410, hereby incorporated by reference, discloses reinforced composite resins having improved handling characteristics by using poly methyl methacrylate (PMMA) in the matrix resin. Products made under this patent have PMMA in the matrix and also in a sheath surrounding the fiber bundle. Consequently, the surface is dry and does not adhere well when layering multiple strips during the fabrication of dental restorations. Alternatively, it is recommended that the strip surface be pre-wetted with liquid material, which results in a weak interphase between multiple strips producing a potentially weak restoration.
It would be desirable to provide a dental material fabricated of resin-impregnated composites and having good formability and handling. It would beneficial that the dental material also exhibit adequate mechanical properties.